1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_JUMP_LABEL_H
3#define _LINUX_JUMP_LABEL_H
4
5/*
6 * Jump label support
7 *
8 * Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com>
9 * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra
10 *
11 * DEPRECATED API:
12 *
13 * The use of 'struct static_key' directly, is now DEPRECATED. In addition
14 * static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following:
15 *
16 * struct static_key false = STATIC_KEY_INIT_FALSE;
17 * struct static_key true = STATIC_KEY_INIT_TRUE;
18 * static_key_true()
19 * static_key_false()
20 *
21 * The updated API replacements are:
22 *
23 * DEFINE_STATIC_KEY_TRUE(key);
24 * DEFINE_STATIC_KEY_FALSE(key);
25 * DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);
26 * DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count);
27 * static_branch_likely()
28 * static_branch_unlikely()
29 *
30 * Jump labels provide an interface to generate dynamic branches using
31 * self-modifying code. Assuming toolchain and architecture support, if we
32 * define a "key" that is initially false via "DEFINE_STATIC_KEY_FALSE(key)",
33 * an "if (static_branch_unlikely(&key))" statement is an unconditional branch
34 * (which defaults to false - and the true block is placed out of line).
35 * Similarly, we can define an initially true key via
36 * "DEFINE_STATIC_KEY_TRUE(key)", and use it in the same
37 * "if (static_branch_unlikely(&key))", in which case we will generate an
38 * unconditional branch to the out-of-line true branch. Keys that are
39 * initially true or false can be using in both static_branch_unlikely()
40 * and static_branch_likely() statements.
41 *
42 * At runtime we can change the branch target by setting the key
43 * to true via a call to static_branch_enable(), or false using
44 * static_branch_disable(). If the direction of the branch is switched by
45 * these calls then we run-time modify the branch target via a
46 * no-op -> jump or jump -> no-op conversion. For example, for an
47 * initially false key that is used in an "if (static_branch_unlikely(&key))"
48 * statement, setting the key to true requires us to patch in a jump
49 * to the out-of-line of true branch.
50 *
51 * In addition to static_branch_{enable,disable}, we can also reference count
52 * the key or branch direction via static_branch_{inc,dec}. Thus,
53 * static_branch_inc() can be thought of as a 'make more true' and
54 * static_branch_dec() as a 'make more false'.
55 *
56 * Since this relies on modifying code, the branch modifying functions
57 * must be considered absolute slow paths (machine wide synchronization etc.).
58 * OTOH, since the affected branches are unconditional, their runtime overhead
59 * will be absolutely minimal, esp. in the default (off) case where the total
60 * effect is a single NOP of appropriate size. The on case will patch in a jump
61 * to the out-of-line block.
62 *
63 * When the control is directly exposed to userspace, it is prudent to delay the
64 * decrement to avoid high frequency code modifications which can (and do)
65 * cause significant performance degradation. Struct static_key_deferred and
66 * static_key_slow_dec_deferred() provide for this.
67 *
68 * Lacking toolchain and or architecture support, static keys fall back to a
69 * simple conditional branch.
70 *
71 * Additional babbling in: Documentation/staging/static-keys.rst
72 */
73
74#ifndef __ASSEMBLY__
75
76#include <linux/types.h>
77#include <linux/compiler.h>
78#include <linux/cleanup.h>
79
80extern bool static_key_initialized;
81
82#define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized, \
83 "%s(): static key '%pS' used before call to jump_label_init()", \
84 __func__, (key))
85
86struct static_key {
87 atomic_t enabled;
88#ifdef CONFIG_JUMP_LABEL
89/*
90 * Note:
91 * To make anonymous unions work with old compilers, the static
92 * initialization of them requires brackets. This creates a dependency
93 * on the order of the struct with the initializers. If any fields
94 * are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need
95 * to be modified.
96 *
97 * bit 0 => 1 if key is initially true
98 * 0 if initially false
99 * bit 1 => 1 if points to struct static_key_mod
100 * 0 if points to struct jump_entry
101 */
102 union {
103 unsigned long type;
104 struct jump_entry *entries;
105 struct static_key_mod *next;
106 };
107#endif /* CONFIG_JUMP_LABEL */
108};
109
110#endif /* __ASSEMBLY__ */
111
112#ifdef CONFIG_JUMP_LABEL
113#include <asm/jump_label.h>
114
115#ifndef __ASSEMBLY__
116#ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
117
118struct jump_entry {
119 s32 code;
120 s32 target;
121 long key; // key may be far away from the core kernel under KASLR
122};
123
124static inline unsigned long jump_entry_code(const struct jump_entry *entry)
125{
126 return (unsigned long)&entry->code + entry->code;
127}
128
129static inline unsigned long jump_entry_target(const struct jump_entry *entry)
130{
131 return (unsigned long)&entry->target + entry->target;
132}
133
134static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
135{
136 long offset = entry->key & ~3L;
137
138 return (struct static_key *)((unsigned long)&entry->key + offset);
139}
140
141#else
142
143static inline unsigned long jump_entry_code(const struct jump_entry *entry)
144{
145 return entry->code;
146}
147
148static inline unsigned long jump_entry_target(const struct jump_entry *entry)
149{
150 return entry->target;
151}
152
153static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
154{
155 return (struct static_key *)((unsigned long)entry->key & ~3UL);
156}
157
158#endif
159
160static inline bool jump_entry_is_branch(const struct jump_entry *entry)
161{
162 return (unsigned long)entry->key & 1UL;
163}
164
165static inline bool jump_entry_is_init(const struct jump_entry *entry)
166{
167 return (unsigned long)entry->key & 2UL;
168}
169
170static inline void jump_entry_set_init(struct jump_entry *entry, bool set)
171{
172 if (set)
173 entry->key |= 2;
174 else
175 entry->key &= ~2;
176}
177
178static inline int jump_entry_size(struct jump_entry *entry)
179{
180#ifdef JUMP_LABEL_NOP_SIZE
181 return JUMP_LABEL_NOP_SIZE;
182#else
183 return arch_jump_entry_size(entry);
184#endif
185}
186
187#endif
188#endif
189
190#ifndef __ASSEMBLY__
191
192enum jump_label_type {
193 JUMP_LABEL_NOP = 0,
194 JUMP_LABEL_JMP,
195};
196
197struct module;
198
199#ifdef CONFIG_JUMP_LABEL
200
201#define JUMP_TYPE_FALSE 0UL
202#define JUMP_TYPE_TRUE 1UL
203#define JUMP_TYPE_LINKED 2UL
204#define JUMP_TYPE_MASK 3UL
205
206static __always_inline bool static_key_false(struct static_key *key)
207{
208 return arch_static_branch(key, false);
209}
210
211static __always_inline bool static_key_true(struct static_key *key)
212{
213 return !arch_static_branch(key, true);
214}
215
216extern struct jump_entry __start___jump_table[];
217extern struct jump_entry __stop___jump_table[];
218
219extern void jump_label_init(void);
220extern void jump_label_init_ro(void);
221extern void jump_label_lock(void);
222extern void jump_label_unlock(void);
223extern void arch_jump_label_transform(struct jump_entry *entry,
224 enum jump_label_type type);
225extern bool arch_jump_label_transform_queue(struct jump_entry *entry,
226 enum jump_label_type type);
227extern void arch_jump_label_transform_apply(void);
228extern int jump_label_text_reserved(void *start, void *end);
229extern bool static_key_slow_inc(struct static_key *key);
230extern bool static_key_fast_inc_not_disabled(struct static_key *key);
231extern void static_key_slow_dec(struct static_key *key);
232extern bool static_key_slow_inc_cpuslocked(struct static_key *key);
233extern void static_key_slow_dec_cpuslocked(struct static_key *key);
234extern int static_key_count(struct static_key *key);
235extern void static_key_enable(struct static_key *key);
236extern void static_key_disable(struct static_key *key);
237extern void static_key_enable_cpuslocked(struct static_key *key);
238extern void static_key_disable_cpuslocked(struct static_key *key);
239extern enum jump_label_type jump_label_init_type(struct jump_entry *entry);
240
241/*
242 * We should be using ATOMIC_INIT() for initializing .enabled, but
243 * the inclusion of atomic.h is problematic for inclusion of jump_label.h
244 * in 'low-level' headers. Thus, we are initializing .enabled with a
245 * raw value, but have added a BUILD_BUG_ON() to catch any issues in
246 * jump_label_init() see: kernel/jump_label.c.
247 */
248#define STATIC_KEY_INIT_TRUE \
249 { .enabled = { 1 }, \
250 { .type = JUMP_TYPE_TRUE } }
251#define STATIC_KEY_INIT_FALSE \
252 { .enabled = { 0 }, \
253 { .type = JUMP_TYPE_FALSE } }
254
255#else /* !CONFIG_JUMP_LABEL */
256
257#include <linux/atomic.h>
258#include <linux/bug.h>
259
260static __always_inline int static_key_count(struct static_key *key)
261{
262 return raw_atomic_read(&key->enabled);
263}
264
265static __always_inline void jump_label_init(void)
266{
267 static_key_initialized = true;
268}
269
270static __always_inline void jump_label_init_ro(void) { }
271
272static __always_inline bool static_key_false(struct static_key *key)
273{
274 if (unlikely_notrace(static_key_count(key) > 0))
275 return true;
276 return false;
277}
278
279static __always_inline bool static_key_true(struct static_key *key)
280{
281 if (likely_notrace(static_key_count(key) > 0))
282 return true;
283 return false;
284}
285
286static inline bool static_key_fast_inc_not_disabled(struct static_key *key)
287{
288 int v;
289
290 STATIC_KEY_CHECK_USE(key);
291 /*
292 * Prevent key->enabled getting negative to follow the same semantics
293 * as for CONFIG_JUMP_LABEL=y, see kernel/jump_label.c comment.
294 */
295 v = atomic_read(&key->enabled);
296 do {
297 if (v < 0 || (v + 1) < 0)
298 return false;
299 } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));
300 return true;
301}
302#define static_key_slow_inc(key) static_key_fast_inc_not_disabled(key)
303
304static inline void static_key_slow_dec(struct static_key *key)
305{
306 STATIC_KEY_CHECK_USE(key);
307 atomic_dec(&key->enabled);
308}
309
310#define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
311#define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
312
313static inline int jump_label_text_reserved(void *start, void *end)
314{
315 return 0;
316}
317
318static inline void jump_label_lock(void) {}
319static inline void jump_label_unlock(void) {}
320
321static inline void static_key_enable(struct static_key *key)
322{
323 STATIC_KEY_CHECK_USE(key);
324
325 if (atomic_read(&key->enabled) != 0) {
326 WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
327 return;
328 }
329 atomic_set(&key->enabled, 1);
330}
331
332static inline void static_key_disable(struct static_key *key)
333{
334 STATIC_KEY_CHECK_USE(key);
335
336 if (atomic_read(&key->enabled) != 1) {
337 WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
338 return;
339 }
340 atomic_set(&key->enabled, 0);
341}
342
343#define static_key_enable_cpuslocked(k) static_key_enable((k))
344#define static_key_disable_cpuslocked(k) static_key_disable((k))
345
346#define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) }
347#define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) }
348
349#endif /* CONFIG_JUMP_LABEL */
350
351DEFINE_LOCK_GUARD_0(jump_label_lock, jump_label_lock(), jump_label_unlock())
352
353#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
354#define jump_label_enabled static_key_enabled
355
356/* -------------------------------------------------------------------------- */
357
358/*
359 * Two type wrappers around static_key, such that we can use compile time
360 * type differentiation to emit the right code.
361 *
362 * All the below code is macros in order to play type games.
363 */
364
365struct static_key_true {
366 struct static_key key;
367};
368
369struct static_key_false {
370 struct static_key key;
371};
372
373#define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, }
374#define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
375
376#define DEFINE_STATIC_KEY_TRUE(name) \
377 struct static_key_true name = STATIC_KEY_TRUE_INIT
378
379#define DEFINE_STATIC_KEY_TRUE_RO(name) \
380 struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
381
382#define DECLARE_STATIC_KEY_TRUE(name) \
383 extern struct static_key_true name
384
385#define DEFINE_STATIC_KEY_FALSE(name) \
386 struct static_key_false name = STATIC_KEY_FALSE_INIT
387
388#define DEFINE_STATIC_KEY_FALSE_RO(name) \
389 struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
390
391#define DECLARE_STATIC_KEY_FALSE(name) \
392 extern struct static_key_false name
393
394#define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \
395 struct static_key_true name[count] = { \
396 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \
397 }
398
399#define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \
400 struct static_key_false name[count] = { \
401 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \
402 }
403
404#define _DEFINE_STATIC_KEY_1(name) DEFINE_STATIC_KEY_TRUE(name)
405#define _DEFINE_STATIC_KEY_0(name) DEFINE_STATIC_KEY_FALSE(name)
406#define DEFINE_STATIC_KEY_MAYBE(cfg, name) \
407 __PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name)
408
409#define _DEFINE_STATIC_KEY_RO_1(name) DEFINE_STATIC_KEY_TRUE_RO(name)
410#define _DEFINE_STATIC_KEY_RO_0(name) DEFINE_STATIC_KEY_FALSE_RO(name)
411#define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name) \
412 __PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name)
413
414#define _DECLARE_STATIC_KEY_1(name) DECLARE_STATIC_KEY_TRUE(name)
415#define _DECLARE_STATIC_KEY_0(name) DECLARE_STATIC_KEY_FALSE(name)
416#define DECLARE_STATIC_KEY_MAYBE(cfg, name) \
417 __PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name)
418
419extern bool ____wrong_branch_error(void);
420
421#define static_key_enabled(x) \
422({ \
423 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \
424 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
425 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
426 ____wrong_branch_error(); \
427 static_key_count((struct static_key *)x) > 0; \
428})
429
430#ifdef CONFIG_JUMP_LABEL
431
432/*
433 * Combine the right initial value (type) with the right branch order
434 * to generate the desired result.
435 *
436 *
437 * type\branch| likely (1) | unlikely (0)
438 * -----------+-----------------------+------------------
439 * | |
440 * true (1) | ... | ...
441 * | NOP | JMP L
442 * | <br-stmts> | 1: ...
443 * | L: ... |
444 * | |
445 * | | L: <br-stmts>
446 * | | jmp 1b
447 * | |
448 * -----------+-----------------------+------------------
449 * | |
450 * false (0) | ... | ...
451 * | JMP L | NOP
452 * | <br-stmts> | 1: ...
453 * | L: ... |
454 * | |
455 * | | L: <br-stmts>
456 * | | jmp 1b
457 * | |
458 * -----------+-----------------------+------------------
459 *
460 * The initial value is encoded in the LSB of static_key::entries,
461 * type: 0 = false, 1 = true.
462 *
463 * The branch type is encoded in the LSB of jump_entry::key,
464 * branch: 0 = unlikely, 1 = likely.
465 *
466 * This gives the following logic table:
467 *
468 * enabled type branch instuction
469 * -----------------------------+-----------
470 * 0 0 0 | NOP
471 * 0 0 1 | JMP
472 * 0 1 0 | NOP
473 * 0 1 1 | JMP
474 *
475 * 1 0 0 | JMP
476 * 1 0 1 | NOP
477 * 1 1 0 | JMP
478 * 1 1 1 | NOP
479 *
480 * Which gives the following functions:
481 *
482 * dynamic: instruction = enabled ^ branch
483 * static: instruction = type ^ branch
484 *
485 * See jump_label_type() / jump_label_init_type().
486 */
487
488#define static_branch_likely(x) \
489({ \
490 bool branch; \
491 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
492 branch = !arch_static_branch(&(x)->key, true); \
493 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
494 branch = !arch_static_branch_jump(&(x)->key, true); \
495 else \
496 branch = ____wrong_branch_error(); \
497 likely_notrace(branch); \
498})
499
500#define static_branch_unlikely(x) \
501({ \
502 bool branch; \
503 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
504 branch = arch_static_branch_jump(&(x)->key, false); \
505 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
506 branch = arch_static_branch(&(x)->key, false); \
507 else \
508 branch = ____wrong_branch_error(); \
509 unlikely_notrace(branch); \
510})
511
512#else /* !CONFIG_JUMP_LABEL */
513
514#define static_branch_likely(x) likely_notrace(static_key_enabled(&(x)->key))
515#define static_branch_unlikely(x) unlikely_notrace(static_key_enabled(&(x)->key))
516
517#endif /* CONFIG_JUMP_LABEL */
518
519#define static_branch_maybe(config, x) \
520 (IS_ENABLED(config) ? static_branch_likely(x) \
521 : static_branch_unlikely(x))
522
523/*
524 * Advanced usage; refcount, branch is enabled when: count != 0
525 */
526
527#define static_branch_inc(x) static_key_slow_inc(&(x)->key)
528#define static_branch_dec(x) static_key_slow_dec(&(x)->key)
529#define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
530#define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
531
532/*
533 * Normal usage; boolean enable/disable.
534 */
535
536#define static_branch_enable(x) static_key_enable(&(x)->key)
537#define static_branch_disable(x) static_key_disable(&(x)->key)
538#define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key)
539#define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key)
540
541#endif /* __ASSEMBLY__ */
542
543#endif /* _LINUX_JUMP_LABEL_H */
544